1. Field of the Invention
The present invention relates to an exposure control apparatus used for a simplified camera in which exposure adjustment is automatically performed in accordance with luminance of a subject.
2. Description of the Related Art
A general camera employs an exposure control apparatus for automatically adjusting a shutter speed and an exposure aperture in accordance with luminance of a subject. Feeding electricity to the exposure control apparatus is carried out by turning on a power-supply switch of the camera. The luminance of the subject is measured when a shutter button is depressed by a half stroke.
Recently, a lens-fitted photo film unit is widely used as a kind of a simplified camera. The lens-fitted photo film unit is loaded with a photo film beforehand when it is manufactured. As for such simplified camera, in order to improve its image quality, an exposure control apparatus being simple and automatic is planned to be incorporated therein. Meanwhile, the lens-fitted photo film unit has advantages that it can be manufactured at low cost and it can be easily used. In view of this, in cameras in which the automatic exposure control apparatus is incorporated, it is not preferable, regarding not only its cost but also its handling, to provide a power-supply switch similarly to the ordinary camera.
By the way, in the lens-fitted photo film unit, a battery is also contained at the time of manufacturing so that the battery is adapted to be incapable of replacement. Thus, if the power-supply switch is omitted to always feed the electric power to the exposure control apparatus, there arises a problem of a waste of the electric power. In particular, this problem cannot be bypassed when the electric power for the exposure control apparatus is supplied from a battery being as a power source for a flash device, even if consumption of the electric power for the exposure control apparatus itself is a little.
In view of the foregoing, it is a primary object of the present invention to provide an exposure control apparatus used for a simplified camera in which a power source is prevented from being wasted without preparing a power-supply switch.
It is a second object of the present invention to provide a simplified camera in which it is possible to take a picture, using an exposure control apparatus.
In order to achieve the above and other objects, the camera according to the present invention comprises the exposure control apparatus including a photometry circuit and a light regulating unit. The photometry circuit measures the luminance of the ambient light and judges whether or not the measured luminance is higher than a prescribed level. When the luminance of the ambient light is judged to be higher than the prescribed level, the light regulating unit reduces the exposure light passing through a taking lens. Feeding the electricity to the exposure control apparatus is carried out in association with a turning-on operation of a flash switch for activating a built-in flash device.
The light regulating unit includes a movable stop plate provided with a small stop opening. This small stop opening is smaller than a fixed stop opening. When the flash switch is turned off, the small stop opening is disposed at an optical path of the taking lens. When the flash switch is turned on and the luminance of the ambient light is the prescribed level or less, the stop plate is evacuated from the optical path by means of a spring. When the flash switch is turned on and the luminance of the ambient light is higher than the prescribed level, the stop plate is returned to the optical path by electromagnetic force against the urging force of the spring so that the small stop opening is disposed at the optical path.
Otherwise, the light regulating unit includes a movable stop plate provided with both of a smaller stop opening and a larger stop opening. The smaller stop opening is smaller than the fixed stop opening, and the larger stop opening is larger than the smaller stop opening. When the flash switch is turned off, the smaller stop opening is disposed at the optical path of the taking lens. When the flash switch is turned on and the luminance of the ambient light is the prescribed level or less, the larger stop opening is disposed at the optical path by means of a spring. When the flash switch is turned on and the luminance of the ambient light is higher than the prescribed level, the smaller stop opening is returned to the optical path by electromagnetic force against the urging force of the spring.
Feeding the electricity to the exposure control apparatus is interrupted when a shutter button is not depressed.